1. Field of the Invention
The present invention relates to an optical data recording and reproducing apparatus that optically reads data from or writes data onto an optical disc. More precisely, the invention relates to a driving apparatus that electromagnetically drives an objective lens thereof.
2. Description of Related Art
In a known optical disc apparatus, such as an opto-magnetic disc apparatus, an objective lens is supported by a carriage that is movable in a radial direction (i.e., tracking direction) of the optical disc. The objective lens is elastically movable in the tracking direction and the focusing direction. A tracking coil and a focusing coil are used to drive the objective lens in the tracking and focusing directions. The tracking coil and focusing coil are provided on a lens holder which holds the objective lens. A magnetic circuit, which constitutes an electromagnetic driving circuit together with the tracking and focusing coils, is provided on the carriage. The focusing and tracking coils are supplied with predetermined directions and intensities of electric current to drive the objective lens holder in a manner such that the laser beams converged by the objective lens correctly trace the recording track of the optical disc.
In the known electromagnetic objective lens driving apparatus, the magnetic circuit on the carriage includes a permanent magnet and a cantilever type yoke member which is secured at one end thereof to the carriage. The yoke member can be opened at the free end side thereof adjacent to the optical disc upon assembly. Thus, assembly can be simplified. Upon assembling, the permanent magnet, and the lens holder, etc., are accommodated in the yoke member, and thereafter, the latter is covered by a magnetic shield plate.
The carriage on which the lens holder and the magnetic circuit are provided should be as light and small as possible in view of the desire for fast access times. The same is true for the magnetic circuit. Namely, the permanent magnet and the yoke member of the magnetic circuit must be as light and small as possible. This however reduces the mechanical strength, thus resulting in occurrence of resonance which has an adverse influence on the precision of the tracking and focusing operations.
Furthermore, in the conventional electromagnetic driving apparatus, there is a large number of components, including the yoke member and the magnetic shield plate separate from the yoke member. This complicates the assembling operation.
The primary object of the present invention is to eliminate the drawbacks of the prior art as mentioned above, by providing a simple, small and light electromagnetic driving apparatus of an objective lens, which has a sufficient mechanical strength and fewer components, and in which no resonance tends to occur.